The high speed door assembly is designed to close over a 3 foot diameter opening within 50 milliseconds of actuation, to contain hazardous materials and vapors within a test fixture. Improvement in the high speed door assembly over prior patented devices is to drastically reduce the mass of the moving parts required. By doing this much lower cylinder pressures are acceptable, and a single explosive bolt can accomplish the required actuation. This also simplifies the sealing requirements and the piston, and the mass and complexity of the supporting structure of the door. The total weight of the moving parts is estimated at 145 pounds. The required gas pressure for acceleration of these parts to attain the required closure time is 800 psi, with nitrogen as the gas medium. This is a 600% lower working pressure than similar devices with heavy steel door elements.